1. Field of the Invention
The present invention relates to a suspension system for an automotive vehicle and, more particularly, to a suspension system for an automotive vehicle so adapted as to control an angle of a roll, i.e. a rolling angle, of the vehicle body by supplying or discharging operating fluid to or from a cylinder interposed between the vehicle body and each of the wheels.
2. Description of the Related Art
For example, as disclosed in Japanese Patent Laid-open Publication (kokai) No. 130,418/1988, there is known a suspension system of the automotive vehicle which allows the vehicle height of the vehicle body to be alterable by controlling the supply or discharge of operating fluid to or from a liquid pressure cylinder interposed between the vehicle body and each of the wheels.
A so-called active control suspension system of this kind is arranged to absorb vibration of a low frequency from a road surface by basically changing the vehicle height of the vehicle body. On the other hand, generally, vibration of a high frequency is absorbed by a gas spring inserted through a liquid pressure chamber of the liquid pressure cylinder. Japanese Patent Laid-open Publication (kokai) No. 38,130/1990 discloses such an active control suspension system with the gas spring. This active control suspension system can suppress the vehicle body from rolling during cornering so as to make a rolling angle of the vehicle body zero or substantially zero. In other words, when the vehicle body is cornering, the operating fluid is supplied to the liquid pressure cylinder on the outer wheel side or discharged from the liquid pressure cylinder on the inner wheel side, thereby making the vehicle height of the vehicle body on the outer wheel side equal to the vehicle height thereof on the inner wheel side.
Heretofore, in order to suppress the vehicle body from rolling, the quantity of the operating fluid to be supplied to the liquid pressure cylinder on the outer wheel side is set to become equal to the quantity of the operating fluid to be discharged from the liquid pressure cylinder on the inner wheel side.
This arrangement, however, may sometimes raise the vehicle height of the vehicle body on the outer wheel side to the contrary, in particular when the vehicle body is cornering at a sharp angle.